Conventional gas turbines used for civil aircraft typically have two electrical generators associated with a spool of the engine. The favoured spool by many gas turbine manufacturers and air framers is the high pressure spool because the operating speed range is reduced compared to the lower pressure spools. The reduced speed range is preferable because the electrical frequency outputted by the generators is proportional to spool speed and a large frequency range can be problematic. Also, having a larger speed range generally results in larger, heavier electrical machines.
Some schemes are known in which the lower speed spools are used to provide rotational drives for electrical generators, but these all require some form of electronic control or complex and heavy gearbox arrangements to provide an acceptable electrical output over the broader speed range. Examples of such schemes are described in US20070151258, US2006272313, US2009051219 and U.S. Pat. No. 5,867,979.
The present invention seeks to provide a gas turbine engine with an improved electrical generating capability.